Method of making tennis cords



Jan. 1965 A. E. 'r. NEALE ETAL 3,

METHOD OF MAKING TENNIS CORDS Filed June 17, 1963 In vemors Alberl:NQGJQ, grin C. Rober'zs B MZQMQMQ M I'M-i: orrreys United States Patent3,164,952 METHOD OF MAKING TENNIS CORDS Albert Edward Toney Neale,Sutton Coldfield, and Brian Charles Roberts, Woodford Green, Essex,England, assiguors to Dunlo'p' Rubber Company Limited, London, England,a British company Filed June 17, 1963, Ser. No. 288,399 Claims priority,application Great Britain, July 3, 1962,

25,400/ 62 13 Claims. (Cl. 57-160) This invention relates toimprovements in cords and especially to cords for the stringing oftennis, badminton and the like racquets.

The properties required in cords if they are to be satisfactory forstringing racquets are such that of the natural filamentary materials,only natural gut has found general acceptance. Gut is, however, veryexpensive and many attempts have therefore been made to produce cordsfrom synthetic filamentary materials.

We have now found that a satisfactory cord can be made by a simplifiedprocess employing saturated steam at high temperature.

According to the invention a method of making cord for the stringing oftennis and the like racquets comprises applying to a monofilamentarytextile core of a synthetic long-chain polymer at least one wrappinglayer of a textile synthetic long-chain polymer material and passing thewrapped core through steam at a pressure of at least 50 pounds persquare inch.

Usually the synthetic long-chain polymer is a fibreforming polymerhaving the formula RXR Y, where R and R are hydrocarbon radicals and Xand Y are amide or ester radicals, such as nylon.

Generally the diameter of the monofilamentary core, which may be asingle monofilament, is from 0.02 to 0.1 inch and each wrapping layer ismade up by a length of monofilament of lesser diameter, usually from0.002 to 0.01 inch.

The helix angle of the wrapping should be between 30 and 70 andpreferably about 40 to 50 with respect to the transverse axis of thecore and the wrapping may be applied as a ribbon of filaments in side byside relationship. In cases where more than one layer of wrapping isapplied adjacent layers are wrapped in opposite directions, oneclockwise and the other counterclockwise.

In order to bond the wrapping together and to the core so as to form acohesive uniform cord both the steam pressure and the time during whichthe wrapped core is exposed to the steam must be accurately controlled.This is conveniently achieved in a continuous process in which thewrapped core is passed at a constant rate through a tube through whichsaturated steam is passed; the rate of travel and the steam pressure areadjusted so that the desired surface softening and bonding of thewrapping is obtained without detriment to the strength of the resultantcord. The bonding should be suflicient to allow sharp kinking andknotting of the cord without separation of the wrapping.

The invention will be further described in examples with reference tothe accompanying drawings in which:

FIGURE 1 shows the steps in forming a cord and FIGURE 2 shows theconstruction of a cord formed by a monofilament core wrapped with twolayers of monofilaments.

A monofilament core 1 of polycaprolactam having a diameter of 0.035 inchwas drawn from a reel 2 by a driving pulley 3 and helically wrapped withtwo layers 4, 5 of monofilament caprolactam 0.005 inch in diameter. Thefirst layer 4 was applied as a ribbon 6 of fifteen filaments 7 at anangle of 50 to the transverse axis of 3,164,952 Patented an. 12, 1965the core in. a clockwise direction and the second layer 5 was applied asa ribbon 8 of twenty filaments 9 in a counter-clockwise direction at asimilar angle. The wrapped core had a diameter of 0.06 inch.

The wrapped core was then passed at a rate of seven feet per minutethrough a tube 10 one foot long containing saturated steam at a pressureof 60 pounds per square inch under a tension of 3 pounds, and drawn overa free running pulley 11 onto a reel 12.

The wrappings of the resultant cord were sufficiently bonded to preventseparation when the cord was kinked sharply.

In a further example a multifilament core of seven 840 denier nylonyarns was braided with sixteen 210 denier nylon yarns one of which wascoloured red and another black. The braided cord had a diameter of 0.073inch.

The wrapped core was then passed at a rate of 7 feet per minute throughthe tube containing saturated steam at a pressure of 85 pounds persquare inch under a tension of 3 pounds.

The braiding of the cord was fused together satisfactorily whilstretaining the pattern of the coloured yarns, the

' stiffness and coherence of the braiding being increased by the steamtreatment.

The tube 10 employed in the above examples was fitted at each end withscrew threaded brass plugs 13, 14 drilled with an 0.075 inch aperture toallow passage of the wrapped cord, which was threaded through the plug13, passed through the tube 10 and threaded through the other plug 14before screwing the plugs into the tube. The tube was also provided witha steam supply cock 15, a pressure gauge 16 and a steam exhaust cock 17.The tube 10 was mounted horizontally with the exhaust cock 17 at thelowermost portion; if it is desired to mount the tube vertically a steamtrap should be provided at the lower end.

The process of the invention was simpler, more readily controlled andless expensive than a prior process involving the use of a phenoladhesive, the resultant cord was also more suitable. in colour than thatproduced by the prior process. Cords of highly translucent appearancecan be produced by the process of the invention.

Having now described our invention, what we claim is:

l. A method of making cord for the stringing of tennis and the likeracquets comprising applying directly to a monofilamentary textile coreof a synthetic long-chain polymer at least one wrapping layer of atextile synthetic long-chain polymer material, and passing the wrappedcore through steam at a pressure of at least 50 pounds per square inchfor a period of time sufiicient to fuse the wrapping layer to the core.

2. A method as claimed in claim 1 wherein the core has a diameter offrom 0.02 to 0.1 inch.

3. A method as claimed in claim 1 wherein the textile core is a singlemonofilament.

4. A method as claimed in claim 3 wherein the textile core is of afiber-forming polymer having the formula RXR Y, where R and R arehydrocarbon radicals and X and Y are members of the class consisting ofamide radicals and ester radicals.

5. A method as claimed in claim 4 wherein each wrapping layer is of afibre-forming polymer having the formula RXR Y, where R and R arehydrocarbon radicals and X and Y are members selected from the classconsisting of amide radicals and ester radicals.

6. A method as claimed in claim 2 wherein each wrapping layer is alength of single monofilament.

7. A method as claimed in claim 1 wherein the wrapping layer is appliedat an angle of from 30 to 70 degrees ping layer is applied at an angleof from 40 to 50 degrees with respect to the transverse axis of thecore.

9. A method as claimed in claim 7 wherein the wrapping is applied as aribbon of filaments in side by side relationship.

10. A method as claimed in claim 1 wherein more than one wrapping layeris applied to the core, adjacent layers being wrapped in oppositedirections, one clockwise and the other anti-clockwise.

11. A method as claimed in claim 1 wherein a wrapping layer of braid isapplied to the core.

12. A method as claimed in claim 1 wherein tension is applied to thewrapped core whilst it is passed through the steam.

13. A method according to claim 6 wherein the single monofilament has adiameter of from 0.002 to 0.01 inch.

References Cited by the Examiner MERVIN STEIN, Primary Examiner.

1. A METHOD OF MAKING CORD FOR THE STRINGING OF TENNIS AND THE LIKERACQUETS COMPRISING APPLYING DIRECTLY TO A MONOFILAMENTARY TEXILE COREOF A SYNTHETIC LONG-CHAIN POLYMER AT LEAST ONE WRAPPING LAYER OF ATEXILE SYNTHETIC LONG-CHAIN POLYMER MATERIAL, AND PASSING THE WRAPPEDCORE THROUGH STEAM AT A PRESSURE OF AT LEAST 50 POUNDS PER SQUARE INCHFOR PERIOD OF TIME SUFFICIENT TO FUSE THE WRAPPING LAYER TO THE CORE.